The invention relates to a dental X-ray diagnostic installation comprising an exposure unit rotatable around vertical axes and including an X-ray tube and cassette holder, and comprising a head support lying between the X-ray tube and cassette holder, for producing general or overall exposures, in which a radiation detector is attached to the cassette holder, the radiation detector supplying an electrical signal corresponding to the dose rate when it is struck by X-rays and which is interconnected to setting means and a dose rate regulator to form an automatic exposure unit, being inter-connected in such manner that the X-ray tube voltage is influenced by the output signal of the radiation detector for the purpose of controlling the dose rate to a value producing an optimum film blackening.
An X-ray diagnostic installation of this type is disclosed in U.S. Pat. No. 4,021,672 issued May 3, 1977. Given this X-ray diagnostic installation, the setting of the exposure values, particularly of the X-ray tube voltage and/or of the X-ray tube current are accordingly adapted to the density (transmissivity) conditions of the patient in such manner that the mean radiation dose influencing the individual film sections is maintained constant. The density can fluctuate relatively greatly within the examined area of the patient. Relatively great differences of density also particularly derive between individual patients, for example between children and adults. Accordingly, a relatively large range of adjustment results when the radiation dose is held constant only by controlling the described exposure parameters.